When Vivian's ult is up, combo your Fire Spit and Salvo on her. The AoE damage will seriously hurt her and her ult drones, if not outright kill. If you can't get close enough, poke her from a distance.
In a straight DPS fight, Vivian does more damage than Zhin. If you have Deflector Shield up, you're likely to win the 1v1. Be wary of his ultimate and Whirl, as both will ignore your shield and the latter can place him behind you.